Various reinforcing materials have been used to increase the strength of rubber articles, including tires, hoses, and the like. Metallic wire, and in particular brass coated steel wire is commonly used as a reinforcement. A primary requirement for effective reinforcement is that the reinforcing material remain tightly bonded to the rubber. Good adhesion is difficult to achieve where, as in the case of a tire, the article is subject to continuous flexing and exposure to high temperatures during use. High initial adhesion may be obtained by providing good mechanical contact between the rubber and the wire during vulcanization but, upon aging and use of the article, the bond strength lessens. To accomplish this, adhesion promoters are commonly used which can increase the level of adhesion between the rubber and the metal. The promoters are commonly added to the rubber compounding recipe prior to vulcanization.
U.S. Pat. No. 3,517,722 to Endter, et al, discloses rubber modified with a resin formed in situ from the reaction of a methylene donor and a methylene acceptor. The donor includes substituted melamine while the acceptor may be m-aminophenol or a resorcinol. Harvey in U.S. Pat. No. 3,992,334 and Thompson in U.S. Pat. No. 4,038,220 also teach the in situ reaction between a substituted melamine and various methylene acceptors to form adhesion promoters for rubber compounds. Bezwada in U.S. Pat. No. 4,539,359. teaches the use of a substituted melamine alone as an adhesion promoter in rubber. Elmer, in U.S. Pat. No. 4,338,263 and Schloman in U.S. Pat. No. 4,436,853 teach the use of the reaction products obtained by reacting a N-(substituted oxymethyl)melamine with a bisphenol and a substituted phenol, respectively, formed outside the rubber compound.
Unfortunately some of these adhesion promoters retard the vulcanization rate. It is therefore desirable that adhesion promoters be developed which have a reduced retardation effect.